Method and device for controlling maneuverability of vehicle

ABSTRACT

In accordance with a vehicle motion control apparatus, a steering angle (θh) of a steering wheel is determined on the basis of a rotation angle (θpm) of an assist motor ( 24   m ) detected by a rotation angle sensor ( 24   s ) and a rotation angle (θvm) of a gear ratio variable motor ( 32   m ) detected by a rotation angle sensor ( 32   s ), and a VGRS control process ( 40   a ) of a gear ratio variable mechanism is executed on the basis of the determined steering angle (θh). Accordingly, since the steering angle (θh) of the steering wheel is determined on the basis of the rotation angle (θvm) used for the VGRS control process ( 40   a ) of the gear ratio variable mechanism and the rotation angle (θpm) used for an EPS control process ( 30   a ) of an EPS actuator, it is possible to obtain the steering angle (θh) of the steering wheel without a steering angle sensor. Therefore, it is possible to reduce the number of the parts of a vehicle motion control apparatus.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. JP 2002-126716. The contents of theseapplications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to motion control method of vehicle andmotion control apparatus of vehicle.

DESCRIPTION OF RELATED ART

As a vehicle motion control apparatus including a transmission ratiochanging mechanism for changing the transmission ratio by driving a gearratio variable motor, provided a way of a steering transmission systemwhich connects a steering wheel to steered wheels, a vehicle motioncontrol apparatus 100 which comprises a steering wheel 21, a firststeering shaft 22, a second steering shaft 23, an EPS actuator 24, rods25, a steering angle sensor 26, a vehicle velocity sensor 27, a torquesensor 28, an EPS_ECU 30, a gear ratio changing mechanism 32, a VGRS_ECU40 and the like, as shown in FIG. 4 and FIG. 5, is available. In themeantime, such “a transmission ratio changing mechanism for changing atransmission ratio by driving an electric motor, located halfway of asteering transmission system which connects the steering wheel 21 to thesteered wheels” is sometimes called variable gear ratio system (referredto as VRS, hereinafter) depending on a case.

That is, an end of the first steering shaft 22 is connected to thesteering wheel 21 and an input side of the gear ratio changing mechanism32 is connected to the other end side of this first steering shaft 22.This gear ratio changing mechanism 32 comprises a gear ratio variablemotor 32 m, a reduction gear 32 g and the like. An end side of thesecond steering shaft 23 is connected to this output side of the gearratio changing mechanism and an input side of the EPS actuator 24 isconnected to the other end side of the second steering shaft 23. The EPSactuator 24 is an electric type powered steering system, which iscapable of converting a rotary motion inputted by the second steeringshaft 23 through a rack and pinion gear (not shown) and the like to amotion in the axial direction of the rods 25 and outputting it. Further,this EPS actuator 24 generates an assist force depending on a steeringcondition by means of an assist motor 24 m which is controlled by theEPS_ECU 30 so as to assist steering by a driver. A rotation angle(steering angle) of the first steering shaft 22 is detected by asteering angle sensor 26 and inputted to the VGRS_ECU 40 as a steeringangle signal θh. A steering torque by the second steering shaft 23 isdetected by a torque sensor 28 and inputted to the EPS control process30 a as a torque signal Tp. Further, a vehicle velocity is detected by avehicle velocity sensor 27 and inputted to the EPS_ECU 30 and VGRS_ECU40 as a vehicle velocity signal V. Further, steered wheels (not shown)are attached to the rods 25.

With such a structure, ratio between input gear and output gear ischanged depending on vehicle velocity at real time by means of a gearratio variable motor 32 m and reduction gear 32 g in the gear ratiochanging mechanism 32 and VGRS_ECU 40 so as to change a ratio of outputangle of the second steering shaft 23 relative to the steering angle ofthe first steering shaft 22. The EPS actuator 24 and the EPS_ECU 30generate an assist force for assisting steering of the vehicle driver bymeans of an assist motor 24 m depending on vehicle driver's steeringcondition and vehicle velocity detected by means of the torque sensor 28and the vehicle velocity sensor 27.

Consequently, the steering gear ratio corresponding to the vehiclevelocity can be set. For example, an output angle by the gear ratiochanging mechanism 32 can be set to be increased with respect to thesteering angle of the steering wheel 21 at the time of vehicle stoppingor traveling at a low velocity. Further, the output angle of the gearratio changing mechanism 32 can be set to be decreased with respect tothe steering angle of the steering wheel 21 at the tite of traveling ata high velocity. Meanwhile, an appropriate assist force corresponding tothe vehicle velocity can be generated by means of an assist motor 24 m.

For example, if a vehicle is stopping or traveling at a low velocity,the steering gear ratio by the gear ratio changing mechanism 32 is setlow and an assist force is intensified by an assist motor 24 m, so thatthe steered wheels can be steered largely even with a light steeringoperation. This facilitates the steering operation of a vehicle driver.On the other hand, if the vehicle is traveling at a high velocity, theassist force by the assist motor 24 m drops and the steering ratio bythe gear ratio changing mechanism 32 is set high. Consequently, thesteering operation becomes heavy and even if the steering wheel isturned largely, it comes that the steered wheels are steered a little.Consequently, it can be expected that vehicle control stability isfurther improved.

However, in a vehicle motion control apparatus 100 mentioned above, asshown in FIG. 5, a lot of sensors such as a steering angle sensor 26, avehicle velocity sensor 27, a torque sensor 28 and the like are employedin addition to a rotation angle sensor 24 s of an assist motor 24 m anda rotation angle sensor 32 s of a gear ratio variable motor 32 m.Accordingly, in the vehicle motion control apparatus 100, an increase ofa product cost is caused by heavy usage of these sensors, and there isfurther a problem that a reduction in a trouble incidence rate isprevented.

On the other hand, taking a motion control performance of the vehicleinto consideration, there is a problem that a control performance of anEPS control process 30 a and a VGRS control process 40 a is lowered, acontrol itself is disabled due to roughness of detection data, in thecase of employing a countermeasure such as simply replacing by aninexpensive sensor having a low resolution, reducing the sensors or thelike.

The present invention is made for the purpose of solving the problemsmentioned above, and an object of the present invention is to provide amotion control method of a vehicle and a motion control apparatus of avehicle which can reduce a number of parts.

Further, another object of the present invention is to provide a motioncontrol method of a vehicle and a motion control apparatus of a vehiclewhich can improve a motion control performance of the vehicle.

DISCLOSURE OF THE INVENTION

In order to achieve the above objects, according to claim 1, a motioncontrol method of a vehicle provided with a transfer ratio variablemechanism for changing a transfer ratio by driving a gear ratio variablemotor, and an assist motor assisting a steering force on the basis of asteering torque generated in an output shaft of the transfer ratiovariable mechanism, in the middle of a steering transfer systemconnecting a steering wheel and steered wheels, comprising:

-   -   a first step of detecting a rotation angle θpm of said assist        motor;    -   a second step of detecting a rotation angle θvm of said gear        ratio variable motor; and    -   a third step of determining a steering angle of said steering        wheel on the basis of the rotation angle θpm detected in        accordance with said first step and the rotation angle θvm        detected in accordance with said second step, wherein said        transfer ratio variable mechanism is controlled on the basis of        the steering angle of said steering wheel determined in        accordance with said third step.

In accordance with a first aspect of the present invention, a steeringangle of a steering wheel is determined on the basis of a rotation angleθpm detected in accordance with a first step and a rotation angle θvmdetected by a second step, and a transfer ratio variable mechanism forchanging a transfer ratio of a steering transfer system is controlled onthe basis of the determined steering angle of the steering wheel.Accordingly, since the steering angle of the steering wheel isdetermined on the basis of the rotation angle θvm used for controllingthe gear ratio variable motor and the rotation angle θpm used forcontrolling the assist motor, it is possible to obtain the steeringangle of the steering wheel without any part for mechanically orelectrically detecting the steering angle such as the steering anglesensor or the like. Therefore, since the part for detecting the steeringangle mentioned above can be abolished, it is possible to reduce thenumber of the parts.

According to claim 2, a motion control method of a vehicle as claimed inclaim 1, wherein the rotation angle is input via the speed reducingmeans to at least one of the detection of the rotation angle θpm inaccordance with said first step and the rotation angleθvm in accordancewith said second step.

In accordance with a second aspect of the present invention, since therotation angle is input via the speed reducing means in the detection ofthe rotation angles θpm and θvm, it is possible to improve a resolutionof the input rotation angles θpm and θvm. Accordingly, since it ispossible to determine the steering angle of the steering wheel on thebasis of the rotation angles θpm and θvm having the high resolution inthe third step described in the first aspect, it is possible to improvethe resolution of the determined steering angles. Therefore, since thecontrol of the transfer ratio variable mechanism is executed on thebasis of the steering angle of the steering wheel having the highresolution, it is possible to improve a motion control performance ofthe vehicle.

According to claim 3, a motion control apparatus of a vehicle providedwith a transfer ratio variable mechanism for changing a transfer ratioby driving a gear ratio variable motor, and an assist motor assisting asteering force on the basis of a steering torque generated in an outputshaft of the transfer ratio variable mechanism, in the middle of asteering transfer system connecting a steering wheel and steered wheels,comprising:

-   -   a first rotation angle detecting means for detecting a rotation        angle θpm of said assist motor;    -   a second rotation angle detecting means for detecting a rotation        angle θvm of said gear ratio variable motor; and    -   a steering angle computing means for determining a steering        angle of said steering wheel on the basis of the rotation angle        θpm detected by said first rotation angle detecting means and        the rotation angle θvm detected by said second rotation angle        detecting means,    -   wherein said transfer ratio variable mechanism is controlled on        the basis of the steering angle of said steering wheel        determined by said steering angle computing means.

In accordance with a third aspect of the present invention, a steeringangle of a steering wheel is determined on the basis of a rotation angleθpm detected by a first rotation angle detecting means and a rotationangle θvm detected by a second rotation angle detecting means, and atransfer ratio variable mechanism for changing a transfer ratio of asteering transfer system is controlled on the basis of the determinedsteering angle of the steering wheel. Accordingly, since the steeringangle of the steering wheel is determined on the basis of the rotationangle θvm used for controlling the gear ratio variable motor and therotation angle θpm used for controlling the assist motor, it is possibleto obtain the steering angle of the steering wheel without any part formechanically or electrically detecting the steering angle such as thesteering angle sensor or the like. Therefore, since the part fordetecting the steering angle mentioned above can be abolished, it ispossible to reduce the number of the parts.

According to claim 4, a motion control method of a vehicle as claimed inclaim 3, wherein the rotation angle is input via the speed reducingmeans to at least one of said first rotation angle detecting means andsaid second rotation angle detecting means.

In accordance with a fourth aspect of the present invention, since therotation angle is input via the speed reducing means to the first andsecond rotation angle detecting means, it is possible to improve aresolution of the input rotation angles. Accordingly, since it ispossible to determine the steering angle of the steering wheel on thebasis of the rotation angles θpm and θvm having the high resolution inthe steering angle computing means described in the third aspect, it ispossible to improve the resolution of the determined steering angles.Therefore, since the control of the transfer ratio variable mechanism isexecuted on the basis of the steering angle of the steering wheel havingthe high resolution, it is possible to improve a motion controlperformance of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a summary of a structure of a vehiclemotion control apparatus;

FIG. 2 is a function block diagram expressing a vehicle motion controlprocess in accordance with EPS_ECU and VGRS_ECU of a vehicle motioncontrol apparatus of the present embodiment;

FIG. 3 is a flow chart showing a flow of a steering angle computingprocess in accordance with VGRS_ECU of the vehicle motion controlapparatus of the present embodiment;

FIG. 4 is a schematic view showing a summary of a structure of aconventional vehicle motion control apparatus; and

FIG. 5 is a function block diagram of the conventional vehicle motioncontrol apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

Descriptions will be given below of an embodiment of a motion controlmethod of a vehicle of the present invention and a vehicle motioncontrol apparatus to which the motion control apparatus of the vehicleis applied. In this case, a vehicle motion control apparatus 20 of thepresent embodiment is the same in a mechanical structure as the vehiclemotion control apparatus 100 mentioned above except the structure thatthe steering angle sensor 26 is deleted from the vehicle motion controlapparatus 100. Accordingly, in the vehicle motion control apparatus 20shown in FIG. 1, the same reference numerals are attached to the samestructure portions as those of the vehicle motion control apparatus 100shown in FIG. 4, and a description thereof will be emitted.

As shown in FIG. 2, in the vehicle motion control apparatus 20 of thisembodiment, two processings, that is, an EPS control process 30 a by theEPS_ECU 30 and VGRS control process 40 a by the VGRS_ECU 40 are carriedout by an electronic control unit (ECU). That is, the vehicle motioncontrol apparatus 20 has a function for controlling the steering gearratio by means of the gear ratio changing mechanism 32 according to VGRScontrol process 40 a with the VGRS_ECU 40, depending on the vehiclevelocity. Further, it has a function of assisting steering by thevehicle driver by generating an assist force depending on steeringcondition by means of the EPS control process 30 a with the EPS_ECU 30.

Accordingly, in a VGRS control process 40 a, a vehicle velocity signal Vgenerated by a vehicle velocity sensor 27 and a steering angle θhdetected by computing as described later are input to a VGRS_ECU 40,whereby there is executed a process of determining a rotation angle of agear ratio variable motor 32 m in a gear ratio variable mechanism 32uniquely defined in correspondence to a vehicle velocity on the basis ofa motor rotation angle map (not shown), and a motor voltage incorrespondence to a determined rotation angle command value is suppliedto the gear ratio variable motor 32 m in accordance with a motor drivecircuit. Therefore, in the gear ratio variable mechanism 32 and theVGRS_ECU 40, a ratio of an output gear with respect to an input gear ischanged in real time in correspondence to a vehicle velocity by the gearratio variable motor 32 m and a reduction gear 32 g.

Further, in an EPS control process 30 a, a steering torque signal Tpgenerated by a torque sensor 28 and the vehicle velocity signal Vgenerated by the vehicle velocity sensor 27 are input to an EPS_ECU 30,whereby there is executed a process of determining a current commandvalue of an assist motor 24 m in an EPS actuator 24 uniquely defined incorrespondence to the vehicle velocity on the basis of a motor currentmap (not shown), and a motor voltage in correspondence to a determinedcurrent command value is supplied to the gear ratio variable motor 32 min accordance with a motor drive circuit. Therefore, in the EPS actuator24 and the EPS_ECU 30, by EPS control process 30 a, an assist force forassisting the steering operation of the driver is generated by theassist motor 24 m, in correspondence to a steering state of the driverand a vehicle velocity which are detected by the torque sensor 28 andthe vehicle velocity sensor 27.

Respective function summaries of each of an EPS control process 30 a bythe EPS_ECU 30 and a VGRS control process 40 a by the VGRS_ECU 40 arebasically the same as the vehicle motion control process by the vehiclemotion control apparatus 100 mentioned above. However, the vehiclemotion control apparatus 20 of the present embodiment is different fromthe conventional vehicle motion control apparatus 100 in a point that asteering angle θh is determined in accordance with a computing processby the VGRS_ECU 40 in place of using the value detected by the steeringangle sensor, and the computed value is used for a VGRS control process40 a.

In other words, as shown in FIGS. 4 and 5, in the vehicle motion controlapparatus 100, the steering angle θh of the steering wheel 21 ismechanically or electrically detected by the steering angle sensor 26,and the steering angle θh is used for the VGRS control process 40 a. Onthe contrary, in the vehicle motion control apparatus 20, as shown inFIG. 2, the steering angle θh of the steering wheel 21 is determined onthe basis of a rotation angle θpm detected by a rotation angle sensor 24s and a rotation angle θvm detected by a rotation angle sensor 32 s, andthe VGRS control process 40 a is executed on the basis of the determinedsteering angle θh. Accordingly, the steering angle sensor 26 is notrequired.

In specific, since a relation on the basis of the following formula (1)is established between the steering angle θh of the steering wheel 21,the rotation angle θpm of the assist motor 24 m and the rotation angleθvm of the gear ratio variable motor 32 m, the steering angle θh isdetermined by executing an arithmetic process of determining thesteering angle θh of the steering wheel 21 from the formula (1) on thebasis of a formula (2) by means of the VGRS_ECU 40.θh+θvm/Gv=θpm/Gp   (1)θh=θpm/Gp−θvm/Gv   (2)

In the above formulas, Gv is a gear ratio (no-unit number) by the gearratio variable mechanism 32 and is set by the VGRS control process 40 a.Further, Gp is a gear ratio (no-unit number) by the EPS actuator 24 andis set by the EPS control process 30 a.

In the present embodiment, the arithmetic process on the basis of theformula (2) is executed in accordance with the steering angle computingprocess which is repeatedly executed at fixed intervals (for example,every five millisecond) of a predetermined timer interrupt processing orthe like, for example, by the VGRS_ECU 40. Then, a description will begiven of a summary of the steering angle computing process on the basisof FIG. 3.

As shown in FIG. 3, in the steering angle computing process, a processof reading data of the rotation angle θpm of the assist motor 24 m isfirst executed by a step S101 after a predetermined initializingprocess. Since the data of the rotation angle θpm is detected by therotation angle sensor 24 s and input to the VGRS_ECU 40, a data readingis executed by reading the data in accordance with a proper interruptprocessing or the like.

Next, a process of reading the data of the rotation angle θvm of thegear ratio variable motor 32 m is executed by a step S103. Since thedata of the rotation angle θvm is detected by the rotation angle sensor32 s and input to the VGRS_ECU 40, a data reading is executed by readingthe data in accordance with a proper interrupt processing or the like inthe same manner as that of the data of the rotation angle θpm.

In the succeeding step S105, a process of reading the data of the gearratios Gp and Gv is executed. The gear ratio Gp is obtained bymultiplying a gear ratio generated by a ball screw interposing betweenan output shaft of the gear ratio variable motor 32 m and a rack shaft,by a gear ratio generated by a pinion gear engaged with a rack of therack shaft, and is set by a design value or a measured value. Further,the gear ratio Gv is set on the basis of a parameter determined by theVGRS control process 40 a.

In this case, the gear ratio obtained by multiplying the gear ratiogenerated by the ball screw interposing between the output shaft of theassist motor 24 m and the rack shaft, by the gear ratio generated by thepinion gear engaged with the rack of the rack shaft corresponds to areduction gear ratio serving as a reduction gear interposing in an inputside of the rotation angle sensor 24 s.

Since all of the parameters required for determining the steering angleθh from the formula (2) mentioned above are prepared by executing thereading process of the steps S101, S103 and S105, a process ofcalculating the steering angle θh is executed in the succeeding stepS107 on the basis of the formula (2). Further, the steering angle θhobtained by the step S107 is sent to the VGRS control process 40 a,whereby a series of present steering angle computing process isfinished.

As described above, in accordance with the vehicle motion controlapparatus 20 on the basis of the present embodiment, the steering angleθh of the steering wheel 21 is determined on the basis of the rotationangle θpm of the assist motor 24 m detected by the rotation angle sensor24 s and the rotation angle θvm of the gear ratio variable motor 32 mdetected by the rotation angle sensor 32 s, and the VGRS control process40 a of the gear ratio variable mechanism 32 is executed on the basis ofthe determined steering angle θh. Accordingly, since the steering angleθh of the steering wheel 21 is determined on the basis of the rotationangle θvm used for the VGRS control process 40 a of the gear ratiovariable mechanism 32 and the rotation angle θpm used for the EPScontrol process 30 a of the EPS actuator 24 (the assist motor 24 m), itis possible to obtain the steering angle θh of the steering wheel 21without the steering angle sensor 26 shown in FIG. 4. Accordingly, sincethe steering angle sensor 26 can be abolished it is possible to reducethe number of the parts.

Further, in accordance with the vehicle motion control apparatus 20 onthe basis of the present embodiment, the rotation angle θpm of theassist motor 24 m is detected by the step S101, the rotation angle θvmof the gear ratio variable motor 32 m is detected by the step S103, andthe steering angle θh of the steering wheel 21 is determined on thebasis of the rotation angle θpm and the rotation angle θvm by the stepS107. Further, the VGRS control process 40 a of the gear ratio variablemechanism 32 is executed on the basis of the steering angle θhdetermined by the step S107. Accordingly, since the steering angle θh ofthe steering wheel 21 is determined on the basis of the rotation angleθvm used for the VGRS control process 40 a of the gear ratio variablemechanism 32 and the rotation angle θpm used for the EPS control process30 a of the EPS actuator 24 (the assist motor 24 m), it is possible toobtain the steering angle θh of the steering wheel 21 without thesteering angle sensor 26 shown in FIG. 4. Therefore, since the steeringangle sensor 26 can be abolished, it is possible to reduce the number ofthe parts.

Further, in the vehicle motion control apparatus 20 in accordance withthe present embodiment, the output of the steering angle sensor 26 isnot used for the VGRS control process 40 a as is different from theconventional vehicle motion control apparatus 100 shown in FIG. 4.Accordingly, a response of a control loop of the gear ratio variablemechanism 32 is lowered on the basis of a reduction in a resolution of acurrent command value, for example, generated in the case that thesteering angle sensor 26 employs the steering angle sensor having a lowresolution for the detection angle, and it is possible to inhibit avibration of the steering wheel 21 from being generated due to aresponse delay.

Since the gear ratio obtained by multiplying the gear ratio generated bythe ball screw interposing between the output shaft of the assist motor24 m and the rack shaft, by the gear ratio generated by the pinion gearengaged with the rack of the rack shaft serves as the reduction gearinterposing in the input side of the rotation angle sensor 24 s, therotation angle θpm is input to the rotation angle sensor 24 s detectingthe rotation angle θpm of the assist motor 24 m via the reduction gear.Accordingly, since it is possible to improve the resolution of the inputrotation angle θpm, the steering angle θh of the steering wheel 21 canbe determined on the basis of the rotation angle θpm having the highresolution in the step S107, and the resolution of the determinedsteering angle θh can be improved. Therefore, since the VGRS controlprocess 40 a of the gear ratio variable mechanism 32 is executed on thebasis of the steering angle θh of the steering wheel 21 having the highresolution, it is possible to improve the motion control performance ofthe vehicle.

Further, since a reduction gear 32 g of the gear ratio variablemechanism 32 serves as the reduction gear interposing in the input sideof the rotation angle sensor 32 s, the rotation angle θvm is input tothe rotation angle sensor 32 s detecting the rotation angle θvm of thegear ratio variable motor 32 m via the reduction gear. Accordingly,since it is possible to improve the resolution of the input rotationangle θvm, it is possible to determine the steering angle θh of thesteering wheel 21 on the basis of the rotation angle θvm having the highresolution in the step S107 and it is possible to improve the resolutionof the determined steering angle θh. Therefore, since the VGRS controlprocess 40 a of the gear ratio variable mechanism 32 is executed on thebasis of the steering angle θh of the steering wheel 21 having the highresolution, it is possible to improve the motion control performance ofthe vehicle.

1. A motion control method of a vehicle provided with a transfer ratiovariable mechanism for changing a transfer ratio by driving a gear ratiovariable motor, and an assist motor assisting a steering force on thebasis of a steering torque generated in an output shaft of the transferratio variable mechanism, in the middle of a steering transfer systemconnecting a steering wheel and steered wheels, comprising: a first stepof detecting a rotation angle θpm of said assist motor; a second step ofdetecting a rotation angle θvm of said gear ratio variable motor; and athird step of determining a steering angle of said steering wheel on thebasis of the rotation angle θpm detected in accordance with said firststep and the rotation angle θvm detected in accordance with said secondstep, wherein said transfer ratio variable mechanism is controlled onthe basis of the steering angle of said steering wheel determined inaccordance with said third step.
 2. A motion control method of a vehicleas claimed in claim 1, wherein the rotation angle is input via a speedreducing means to at least one of the detection of the rotation angleθpm in accordance with said first step and the rotation angle θvm inaccordance with said second step.
 3. A motion control apparatus of avehicle provided with a transfer ratio variable mechanism for changing atransfer ratio by driving a gear ratio variable motor, and an assistmotor assisting a steering force on the basis of a steering torquegenerated in an output shaft of the transfer ratio variable mechanism,in the middle of a steering transfer system connecting a steering wheeland steered wheels, comprising: a first rotation angle detecting meansfor detecting a rotation angle θpm of said assist motor; a secondrotation angle detecting means for detecting a rotation angle θvm ofsaid gear ratio variable motor; and a steering angle computing means fordetermining a steering angle of said steering wheel on the basis of therotation angle θpm detected by said first rotation angle detecting meansand the rotation angle θvm detected by said second rotation angledetecting means, wherein said transfer ratio variable mechanism iscontrolled on the basis of the steering angle of said steering wheeldetermined by said steering angle computing means.
 4. A motion controlmethod of a vehicle as claimed in claim 3, wherein the rotation angle isinput via a speed reducing means to at least one of said first rotationangle detecting means and said second rotation angle detecting means.